Nov., 1'347
STUDY OF APPROACHES TO HALOGENATED ORTHOESTERS
[CONTRIBUTION FROM THE
LABORATUKY OF ORGANIC CHEMISrRY OF 'I H E
UNIVERSITY O F
2667
WISCONSIN]
A Study of New A;>proaches to a-Halogenated Orthoesters H Y S. hl. AICELVAIN .IN[) CALVIN L. STEVENS' The removal of the elements of an alkyl hypobromite from an u-bromoorthoester is a t present the only general method that has been found for the preparation of substituted ketene KCH=C(0C2H5)2. An attempt to extend this method to the preparation of such a disubstituted ketene acetal as dimethylketene tiiniethylacetal, (CH3)2C=C(OCH3)2,was unsuccessful becailse the requisite methyl a-bromoorthoisobutyrate could not be prepared : alcoholysis of inethyl cu-bromoiminoisobutyrate hydrochloride yielded only the corresponding amide, and methyl orthoisobutyrate could not be The present paper reports an exploration of some new approaches to the synthesis of an orthoester of an a-haloisobutyric acid. The first of these involved the preparation and alcoholysis of certain N-substi tuted hinoesters of a-chloroisobutyric acid (111), which were obtained by the sequence of reactions, I to I11 (CHI)LHCOXHK 1
PCI:, __f
(CH,)?CClC(CI)=SK
NaOR'
-+
iiiore basic cyclic form VI, which would form a hydrochloride that could be alcoholyzed to an orthoester. When the iminoester V, obtained from the reaction of I1 (K is C2H5) with the monosodium salt of ethylene glycol, was distilled the following products were obtained: I V (R is C2H5), ethylene chlorohydrin ( I X ) , and a chloritic-free residue. The latter material had a wide boiling range arid left considerable non-volatile residue each time it was distilled. These reaction products indicate that the ester V cyclizes to the more basic structure VI, which then dehydrochlorinates another molecule of V (or VI) to form the chlorine-free methiminoacrylate (VII) and the hydrochloride (VI I I ) . Polymerization of VI1 accounts for the non-volatile residue, and pyrolysis of the hydrochloride (VIII) produces I V and IX. (CH~)2CClC(OCH2CHzOH)=XC~H~ + 1-
/NHCrH, (CH3)rCClC-0 C H J
\
\ ---j
I1
14C1 (CH,)~CCIC(OK')=NII ---+ (CHa)2CClCONHR 111 IV
The irninoesters ( I l l , K is CH3; K' is CHs or C2H5) were recovered unchanged after several hours of refluxing in methyl or ethyl alcohols. Since the free irninoesters did not undergo alcoholysis, attempts were made to prepare salts of I11 in order that these might be subjected to alcoholysis. However, 111 was converted directly to the amide (IV) .when treated with dry hydrogen chloride in ether solution with no evidence of the formation of an intermediate hydrochloride. In the hope t h a t these results would be modified if the 0--R' bond of 111 were strengthened, the phenyl ester (111, K is C2H5; K' is C6H5)was prepared. This ester is indeed more stable; i t forms a homogeneous solution with ether containing dry hydrogen chloride (no salt formation) from which most of the ester may be recovered by evaporation of the ether. 'There is some cleavage of the phenoxy group a.s shown by the fact that a srriall amount of the iminochloritle (11, l i is C2HJ accompanies the recovered phenyl iminoester. When this pheiiyl iniirioester is treated with hydrogen chloride in absolute alcohol, it is quantitatively converted to pheiiol arid the amide (IV). The hydroxyethyl iminoestcr V was prepared with the expectation t h a t i t would exist in the (1) Wisconsin .4lumni Research I'c,undation Reaearch Assistant. 1944-1947. (2) Mct*:lvain. r l 0 1 , . ' I ' H I ~ J < , i ' u u . i i , . 62, 1181 (1!140), 64, l ! l W ' I!U2J; 66, I922 ( l 9 4 t i ) . ( 3 ) K e n t . 1% n 'rhr4.;. IJnivrrcity
